BORIS Johnson challenged Theresa May in Cabinet today over her plan to align some of Britain’s rules with the EU’s after Brexit.

A dangerous Tory Brexiteer revolt has also been spiralling tonight over the PM’s proposal, drawn up to break a negotiations deadlock over the Irish border.

Mrs May has offered “a common set of goals” in limited areas such as agriculture and energy to satisfy Dublin’s demand for no hard border.
But to stop Ulster from having a separate settlement, Brexit Secretary David Davis yesterday confirmed to MPs that the arrangement would also apply to the whole of the UK.

While soft Brexiteer Tories welcomed the move as “common sense”, it infuriated hard-line Brexiteers who have demanded a clean break from Brussels.

It has also emerged tonight that Mrs May had not told her Cabinet about her controversial offer in Brussels on Monday, or won its sign off for it.

The Sun has learned that Boris spoke out over his fears about it at the weekly meeting of the PM’s top table of ministers this morning.

Mr Johnson told Mrs May that he “would worry if regulatory alignment bound us into the EU”.

A senior Whitehall source added: “Cabinet is in the dark about what the PM is doing now, which is a very strange state of affairs to be in”.

No10 aides insisted tonight that Boris was reassured that the PM’s offer was only an emergency solution in the “unlikely” scenario that the UK fails to win a good trade deal.

But in another blow to the PM, a former Tory leader has tonight called on her to drop the plan – and walk away from talks if the EU insisted on it.

Iain Duncan-Smith said: “We cannot sign up to regulatory alignment. It means we can’t do trade deals
“These are demands that are designed to box us in. We have to say to them, ‘not good enough’. We simply can’t pay this price.”

But a fresh civil war threatened to engulf the Tory party last night as pro-EU backbenchers hit back at IDS.

Former Education Secretary Nicky Morgan branded his walk away demand “madness”, adding: “Walking away when the Brexiteers encounter difficulties they never bothered to anticipate is not in the national interest and betrays the futures of millions of young people”.

Summoned to the Commons yesterday to explain Brexit talks’ breakdown on Monday, Mr Davis was also forced to insist to MPs that the plan does not mean surrendering rule making powers back to Brussels.

The Brexit Secretary said it would mean “mechanisms such as mutual recognition” instead, adding: “It’s not harmonisation, it’s not being in the single market, it’s not having absolutely the same rules.

“It’s this house exercising its democratic right to choose our own laws in such a way to maximise our ability to sell abroad.”

But Mr Davis raised eyebrows when he also refused a demand from Tory MP Jacob Rees-Mogg to make regulatory divergence a Brexit red line.

Mr Davis instead said: “The red line for me is delivering the best Brexit for Britain”.

With time now running out fast to strike a Brexit divorce deal this year by Friday’s hard deadline, Labour’s shadow Brexit Secretary Keir Starmer branded Monday’s talks breakdown “an embarrassment”.

A former top Foreign Office mandarin also warned the fresh Tory row was “damaging” for Mrs May’s respect in Brussels.

Lord Ricketts said: “It leaves an impression, I think, in Brussels that the Prime Minister hasn’t got authority over her own side and that will knock confidence in doing a final deal.”

Tonight Philip Hammond waded into the row, using a speech to the financial industry to reiterate his support for keeping the closest possible trading relationship with the EU.

And he vowed to get a deal that would be "more ambitious than any existing ere free trade agreement" that reflects our decades-long "common regulatory" alignment.

In a specific pledge to London's financial industry, Mr Hammond said the Government will protect the sector's ability to "operate as a single marketplace.

He also told Paris and Frankfurt to forget about stealing London's place as Europe's financial capital – saying it would only weaken the continent asa while to the advantage of the likes of New York and Singapore.

In an address guaranteed to anger Brexit hardliners, the Chancellor told the CityUK annual dinner: "We will need intensive regulatory cooperation for rule-making to ensure parity of outcomes.

"And we will need new mechanisms to address key cross-cutting issues, from dispute resolution to data protection.

"We will need a deep and comprehensive framework of standards that ensures unprecedented transparency and supervisory cooperation."